Hip fracture is a major public health problem. Results from our previous work demonstrate a 4.6 percent loss of femoral neck bone mineral density (BMD) during the year following a hip fracture; this dramatic loss in BMD is accompanied by notable changes in markers of bone metabolism. The parent project to the proposed ancillary study is a randomized controlled trial of a home-based exercise program intended to minimize losses in BMD, muscle and function following a hip fracture. The proposed ancillary study will evaluate markers of bone metabolism and selected regulating hormones in hip fracture patients who are participating in this intervention study in order to gain a better understanding of the mechanism by which exercise affects bone health during the year following a hip fracture. These markers and hormones also will be evaluated over a one year period in a matched group of non-fracture controls to establish expected levels and changes in markers of bone metabolism among a frail group of older persons who also have low BMD. The primary aims of the proposed study are: 1) to evaluate the role of exercise on bone metabolism following hip fracture by comparing bone metabolism during the year after hip fracture in patients randomized to a home-based exercise intervention with patients assigned to usual care, and 2) to separate the effects of hip fracture on bone metabolism from those of aging in similar persons with low BMD by comparing bone metabolism in hip fracture patients receiving usual care with bone metabolism in a matched group of non-fracture controls. These issues will be addressed using data from 170 female hip fracture patients age 65 plus (100 enrolled in the parent study, and an additional 70 hip fracture patients to be recruited for this ancillary study), and 85 age- and mobility-matched non- fracture controls with BMD Less than 0.82g/cm2. Patients are randomized to a year-long, home-based exercise program to begin when post-acute therapy ends, or usual care. As part of the parent study, 100 patients are having BMD measured during their hospital stay, and again at 2, 6, and 12 months, and blood samples for these 100 patients are being taken, processed, and stored. For the ancillary study, this protocol will be extended to include 70 additional hip fracture patients and 85 non- fracture controls, the latter of which will be measured at point of enrollment and 12 months later. For this ancillary study, all blood samples (i.e., those collected on 100 patients in the parent study and those collected on 70 patients and 85 non- fracture controls in the ancillary study) will be assayed to determine levels of four markers of bone metabolism and three regulating hormones. Information of this type will be useful developing interventions to improve bone health and maximize recovery.